The Doctor is on the tail of a 'Fortean Flicker', a peculiar dimensional anomaly which throws out coincidences, when he gets caught up in a battle between vicious tortoises, a bunch of future hippies and commuters from the 20th century. Meanwhile, the Galaxy's most dangerous criminal is on the trail of something called The Highest Science.
p. 58 The TARDIS lands on Sakkrat AKA Hogsumm.
Benny's first two adventures - Love And War and Transit - get a few mentions here and there but really this is a standalone in the best sense of the word.
p.54 The Archive Tower is a (presumably rather large) building on Gallifrey.
p.59 The Doctor puts on his duffel coat, as seen in the Curse of Fenric.
p.61 When the Doctor is watching Captain Millennium, he notes that it is "almost like real life" when there is a scene that seems to be echoing Sarah-Jane's encounter with the eponymous metallic beast in Robot.
p.66 The Doctor mentions Charlie Parker. The seventh Doctor's love of jazz was established in Silver Nemesis.
p.71 Jan, the Travellers and the Hoothi are all from Love and War.
p.119 Witcher: "It's like something out of that rubbish they used to put on after Grandstand." Doctor Who used to be on after Grandstand.
p.124 The Doctor mentions having no contingency plans, a reference to the seventh Doctor's perceived role as a manipulator who uses time to cheat solutions.
p.168 Hooray for a mention of the sonic screwdriver and its absence since The Visitation. In the next book, The Pit, it suddenly re-appears for no adequately explored reason.
p.170 The Doctor is wearing a blue gemstone ring, but I don't know if this is a reference to another story.
p.171 Benny remembers the Heavenite observatory from Love and War and "Pointing a gun at the Doctor in a tunnel somewhere" from Transit.
p.183 The Doctor mentions that crossing the timelines can leave one sensitive to temporal disturbances, as seen in City of Death.
p.204 One of the guardians notices that something about Benny's name feels false: a reference to Benny's lack of a 'proper' professorship, as established in Love and War.
p.208 The Doctor mentions that he ran Taunton (in Somerset) for two weeks in the 18th century "and I've never been so bored".
OLD FRIENDS AND OLD ENEMIES
None. Even Virginia Woolf doesn't make an appearance.
NEW FRIENDS AND NEW ENEMIES
Introduced for the first time here are the Chelonians, who go on to appear in Zamper and The Well-Mannered War, and get mentions elsewhere. We're also introduced to Shelduker, the galaxy's most dangerous criminal; Gustav Ernst, the (in)famous explorer who gets mentioned in legend quite a bit, including through the Benny NAs; Rosheen and Klift, two immoral computer fraudsters; Sendei, Molassi and Rodomonte, three spaced out hippies from 2112; Checkley's World, home to some gruesome military-style genetic labs; The Cell, a rather revolting product of same; and a lot of out-of-place commuters whose fate is finally resolved in Happy Endings.